Zoom lens system and optical apparatus using the same

Abstract

Providing a zoom lens system being compact and simple having excellent optical performance suitable for an optical apparatus with a limited space for a zoom lens, and capable of shifting an image, and an optical apparatus equipped therewith. The system includes, in order from an object: a first group having positive power and an optical path bending element; a second group having negative power; a third group having positive power; and a fourth group having positive power. Upon zooming from a wide-angle end to a telephoto end, the first and third groups are fixed relative to an image plane, the second group and the fourth group are moved along the optical axis, an image on the image plane can be shifted by shifting the third group or a portion thereof substantially perpendicularly to the optical axis. The first group includes at least one negative lens, and satisfies a given condition.

The invention claimed is: 
     
       1. A zoom lens system consisting of, in order from an object along an optical axis:
 a first lens group having positive refractive power and an optical path bending element; 
 a second lens group having negative refractive power; 
 a third lens group having positive refractive power; and 
 a fourth lens group having positive refractive power; 
 upon varying a focal length from a wide-angle end state to a telephoto end state, the first lens group being fixed with respect to an image plane, a distance between the first lens group and the second lens group increasing, a distance between the second lens group and third lens group decreasing, and a distance between the third lens group and the fourth lens group decreasing, 
 the first lens group including at least one negative lens, and 
 the following conditional expression being satisfied:
   1.900 <nd 1 
 
 
       where nd 1  denotes a refractive index of the negative lens at d-line (wavelength λ=587.6 nm),
 wherein at least one of the third lens group and the fourth lens group consists of, in order from the object along the optical axis, a positive lens having a convex surface facing the object, and a cemented negative lens constructed by a positive lens having a convex surface facing the object cemented with a negative lens having a concave surface facing the image. 
 
     
     
       2. The zoom lens system according to  claim 1 , wherein the third lens group is fixed with respect to the image plane upon varying a focal length from the wide-angle end state to the telephoto end state. 
     
     
       3. The zoom lens system according to  claim 1 , wherein the first lens group includes at least one negative lens, and the following conditional expression is satisfied:
   1.940 <nd 1 
 
       where nd 1  denotes a refractive index of the negative lens at d-line (wavelength λ=587.6 nm). 
     
     
       4. The zoom lens system according to  claim 1 , wherein the first lens group includes at least one negative lens, and the following conditional expression is satisfied:
     νd 1<21.00 
 
       where νd 1  denotes an Abbe number of the negative lens at d-line (wavelength λ=587.6 nm). 
     
     
       5. The zoom lens system according to  claim 1 , wherein the first lens group includes at least one negative lens, and the following conditional expression is satisfied:
   νd1<20.50
 
 
       where νd 1  denotes an Abbe number of the negative lens at d-line (wavelength λ=587.6 nm). 
     
     
       6. The zoom lens system according to  claim 1 , wherein the third lens group includes at least one cemented lens. 
     
     
       7. The zoom lens system according to  claim 1 , wherein the following conditional expression is satisfied:
   0.5 <f 4 /f 3<1.1 
 
       where f 3  denotes a focal length of the third lens group, and f 4  denotes a focal length of the fourth lens group. 
     
     
       8. The zoom lens system according to  claim 1 , wherein the first lens group includes at least one negative lens, the negative lens in the first lens group is a negative meniscus lens having a convex surface facing the object, and the first lens group consists of, in order from the object along the optical axis, the negative meniscus lens, the optical path bending element, and a positive lens having a convex surface facing the object. 
     
     
       9. The zoom lens system according to  claim 1 , wherein the optical path bending element is a rectangular prism and the following conditional expression is satisfied:
   1.800 <ndp    
 
       where ndp denotes a refractive index of the rectangular prism at d-line (wavelength λ=587.6 nm). 
     
     
       10. The zoom lens system according to  claim 1 , wherein the first lens group includes at least one aspherical lens. 
     
     
       11. The zoom lens system according to  claim 1 , wherein the second lens group consists of, in order from the object along the optical axis, a negative lens having a concave surface facing the image, and a cemented negative lens constructed by a negative lens having a concave surface facing the object cemented with a positive lens. 
     
     
       12. The zoom lens system according to  claim 1 , wherein the second lens group includes at least one aspherical lens. 
     
     
       13. The zoom lens system according to  claim 1 , wherein the following conditional expression is satisfied:
   0.8<(− f 2)/ fw< 1.3
 
 
       where fw denotes a focal length of the zoom lens system in the wide-angle end state, and f 2  denotes a focal length of the second lens group. 
     
     
       14. The zoom lens system according to  claim 1 , wherein focusing from infinity to a close object is carried out by moving the second lens group along the optical axis to the object side. 
     
     
       15. The zoom lens system according to  claim 1 , wherein the following conditional expression is satisfied:
   1.5 <f 1/(− f 2)<4.0
 
 
       where f 1  denotes a focal length of the first lens group, and f 2  denotes a focal length of the second lens group. 
     
     
       16. The zoom lens system according to  claim 1 , wherein the third lens group includes at least one aspherical lens. 
     
     
       17. The zoom lens system according to  claim 1 , wherein the fourth lens group includes at least one aspherical lens. 
     
     
       18. The zoom lens system according to  claim 1 , wherein an aperture stop is disposed between the second lens group and the third lens group, and the aperture stop is located adjacent to the object side of the third lens group. 
     
     
       19. A zoom lens system comprising, in order from an object along an optical axis:
 a first lens group having positive refractive power and an optical path bending element; 
 a second lens group having negative refractive power; 
 a third lens group having positive refractive power; and 
 a fourth lens group having positive refractive power; 
 upon varying a focal length from a wide-angle end state to a telephoto end state, the first lens group being fixed with respect to an image plane, a distance between the first lens group and the second lens group increasing, a distance between the second lens group and third lens group decreasing, and a distance between the third lens group and the fourth lens group decreasing, and 
 an image on the image plane being able to be shifted by shifting the third lens group or a portion of the third lens group as a shift lens group in a direction substantially perpendicular to the optical axis, 
 wherein at least one of the third lens group and the fourth lens group consists of, in order from the object along the optical axis, a positive lens having a convex surface facing the object, and a cemented negative lens constructed by a positive lens having a convex surface facing the object cemented with a negative lens having a concave surface facing the image, 
 wherein the first lens group includes at least one negative lens, and the following conditional expression is satisfied:
   1.900 <nd 1 
 
 
       where nd 1  denotes a refractive index of the negative lens in the first lens group at d-line (wavelength λ=587.6 nm). 
     
     
       20. A zoom lens system comprising, in order from an object along an optical axis:
 a first lens group having positive refractive power and an optical path bending element; 
 a second lens group having negative refractive power; 
 a third lens group having positive refractive power; and 
 a fourth lens group having positive refractive power; 
 upon varying a focal length from a wide-angle end state to a telephoto end state, the first lens group being fixed with respect to an image plane, a distance between the first lens group and the second lens group increasing, a distance between the second lens group and third lens group decreasing, and a distance between the third lens group and the fourth lens group decreasing, and 
 an image on the image plane being able to be shifted by shifting the third lens group or a portion of the third lens group as a shift lens group in a direction substantially perpendicular to the optical axis, 
 wherein at least one of the third lens group and the fourth lens group consists of, in order from the object along the optical axis, a positive lens having a convex surface facing the object, and a cemented negative lens constructed by a positive lens having a convex surface facing the object cemented with a negative lens having a concave surface facing the image, 
 wherein the following conditional expression is satisfied:
   0.75 <βbt ×(1−(3 −βat )<1.2
 
 
 
       where βat denotes lateral magnification of the third lens group in the telephoto end state, and βbt denotes lateral magnification of a lens system locating between the third lens group and the image plane in the telephoto end state. 
     
     
       21. The zoom lens system according to  claim 20 , wherein the following conditional expression is satisfied:
   0.3 <fw/f 3<0.5 
 
       where f 3  denotes a focal length of the third lens group, and fw denotes a focal length of the zoom lens system in the wide-angle end state. 
     
     
       22. An optical apparatus equipped with the zoom lens system according to any one of  claims 1 - 21 . 
     
     
       23. A method for varying a focal length of a zoom lens system comprising steps of:
 providing the zoom lens system consisting of, in order from an object along an optical axis, a first lens group having positive refractive power and an optical path bending element, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, the first lens group including at least one negative lens, the negative lens satisfying the following conditional expression:
   1.900 <nd 1 
 
 
       where nd 1  denotes a refractive index of the negative lens at d-line (wavelength λ=587.6 nm), wherein at least one of the third lens group and the fourth lens group consists of, in order from the object along the optical axis, a positive lens having a convex surface facing the object, and a cemented negative lens constructed by a positive lens having a convex surface facing the object cemented with a negative lens having a concave surface facing the image; and
 moving the second lens group and the fourth lens group along the optical axis such that upon varying a focal length from a wide-angle end state to a telephoto end state, the first lens group is fixed with respect to the image plane, a distance between the first lens group and the second lens group increases, a distance between the second lens group and the third lens group decreases, and a distance between the third lens group and the fourth lens group decreases. 
 
     
     
       24. A method for focusing a zoom lens system comprising steps of:
 providing the zoom lens system consisting of, in order from an object along an optical axis, a first lens group having positive refractive power and an optical path bending element, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, upon varying a focal length from a wide-angle end state to a telephoto end state, the first lens group being fixed with respect to the image plane, a distance between the first lens group and the second lens group increasing, a distance between the second lens group and the third lens group decreasing, and a distance between the third lens group and the fourth lens group decreasing, the first lens group including at least one negative lens, and the negative lens satisfying the following conditional expression:
   1.900 <nd 1 
 
 
       where nd 1  denotes a refractive index of the negative lens at d-line (wavelength λ=587.6 nm), wherein at least one of the third lens group and the fourth lens group consists of, in order from the object along the optical axis, a positive lens having a convex surface facing the object, and a cemented negative lens constructed by a positive lens having a convex surface facing the object cemented with a negative lens having a concave surface facing the image; and
 moving the second lens group along the optical axis to the object side to carry out focusing from infinity to a close object. 
 
     
     
       25. A zoom lens system consisting of, in order from an object along an optical axis:
 a first lens group having positive refractive power and an optical path bending element; 
 a second lens group having negative refractive power; 
 a third lens group having positive refractive power; and 
 a fourth lens group having positive refractive power; 
 upon varying a focal length from a wide-angle end state to a telephoto end state, the first lens group being fixed with respect to an image plane, a distance between the first lens group and the second lens group increasing, a distance between the second lens group and third lens group decreasing, and a distance between the third lens group and the fourth lens group decreasing, 
 the first lens group including at least one negative lens, and 
 the following conditional expressions being satisfied:
   1.900 <nd 1 
   1.5 <f 1/(− f 2)<4.0
 
 
 where nd 1  denotes a refractive index of the negative lens at d-line (wavelength λ=587.6 nm), f 1  denotes a focal length of the first lens group, and f 2  denotes a focal length of the second lens group.